Interlinings are the invisible scaffolding of clothing. They ensure correct fit and optimal wearing comfort. Depending on application, they augment processibility, enhance functionality and stabilize clothing. In addition to clothing, these functions can find application in industrial textile applications, for example furniture, upholstery and home textiles.
Important properties required of interlinings are softness, springiness, hand, wash and care durability and also adequate abrasion resistance on the part of the backing material in use.
Interlinings can consist of nonwovens, wovens, formed-loop knits or comparable textile sheet materials, which are usually additionally provided with a bonding compound whereby the interlining can be adhered to a top fabric usually thermally via heat and/or pressure (fusible interlining). The interlining is thus laminated onto a top fabric. The various textile sheet materials mentioned have different property profiles, depending on their method of making Woven fabrics consist of threads/yarns in the warp and weft directions, formed-loop knits consist of threads/yarns connected via a loop construction into a textile sheet material. Nonwovens consist of individual fibers laid down to form a fibrous web which are bonded mechanically, chemically or thermally.
In the case of mechanically nonwovens, the fibrous web is consolidated by mechanical interlacing of the fibers. This utilizes either a needling technique or an interlacing by means of jets of water or vapor. Needling does give soft products, albeit with relatively labile hand, so that this technology has become established for interlinings only in quite specific niches. In addition, mechanical needling requires typically a basis weight>50 g/m2, which is too heavy for a multiplicity of interlining applications.
Nonwovens consolidated using jets of water can be produced in lower basis weights, but generally are flat and lack springiness.
In the case of chemically bonded nonwovens, the fibrous web is treated with a binder (an acrylate binder for example) by impregnating, spraying or by means of other customary methods of application, and subsequently cured. The binder bonds the fibers together to form a nonwoven, but has the consequence that a relatively stiff product is obtained, since the binder is widely distributed throughout the fibrous web and adheres the fibers together throughout as in a composite material of construction. Variations in hand/softness cannot be fully compensated via fiber blends or binder choice.
Thermally bonded nonwovens are typically calender or hot air consolidated for use as interlinings. The current standard technology for nonwoven interlinings is pointwise calender consolidation. The fibrous web here generally consists of polyester or polyamide fibers specifically developed for this process, and is consolidated by means of a calender at temperatures around the melting point of the fiber, one roll of the calender having a point engraving. Such a point engraving consists for example of 64 points/cm2 and can have a sealing surface of 12% for example. Without a point arrangement, the interlining would be consolidated flattish and be unsuitably harsh in hand.
The above-described different processes for producing textile sheet materials are known and described in textbooks and in the patent literature.
The bonding compounds typically applied to interlinings are thermally activatable and consist generally of thermoplastic polymers. The technology for applying these bonding compound coatings is effected according to the prior art in a separate operation onto the fibrous sheet material. By way of bonding compound technology it is typically powder point, paste printing, double point, sprinkling, hotmelt processes which are known and described in the patent literature. Double point coating is currently considered to be the most effective with regard to adherence to the top fabric after caring treatment.
Such a double point has a two-layered construction in that it consists of an underpoint and an overpoint. The underpoint penetrates into the base material and serves as blocking layer against bonding compound strike-back and to anchor the overpoint particles. Customary underpoints consist of for example of binder. Depending on the chemistry used, the underpoint contributes as a blocking layer to the prevention of bonding compound strike back as well as to the anchoring in the base material. It is primarily the overpoint composed of a thermoplastic material which is the main adhesive component in the two-layered composite and which is sprinkled as a powder onto the underpoint. After sprinkling, the excess portion of the powder (between the points of the lower layer) is sucked off again. After subsequent sintering, the overpoint is (thermally) bonded on the underpoint and can serve as adhesive material in respect of the top fabric.
Depending on the intended purpose of the interlining, different numbers of points are printed and/or the amount of bonding compound or the geometry of the point pattern is varied. A typical number of points is, for example, CP 110 for an add-on of 9 g/m2, or CP 52 having an add-on rate of 11 g/m2.
Double-point technology is disadvantageous in that it requires very considerable machinery and invest, since the thermoplastic overpoint material first has to be sprinkled on and then the excess between the points of bonding compound has to be sucked off again, which is inconvenient and costly. If this operation is not accomplished to a sufficient degree, or not at all, unwanted hand harshenings can occur after fusing in the interlining/top fabric laminate, and soiling of the top fabric due to shedded loose polymeric particles and interply sticking due to the absent blocking layer may occur.
Paste printing is also widely used. In this technology, an aqueous dispersion is prepared from thermoplastic polymers, typically in particulate form having a particle size<80 μm, thickeners and flow control agents and is then applied in paste form to the backing ply usually in the form of points by means of a rotary screen printing process. The printed backing ply is subsequently subjected to a drying operation. Paste printing for applying the bonding compound is less good than the double point process in terms of bonding performance and in bonding compound strike-back because of the absent blocking layer.